Method of making plastic boat



Oct. 12, 1965 METHOD OF MAKING PLASTIC BOATS Original Filed March 20,1958 S Sheets-Sheet 1 I\ LAlJulQuM/AMLALALA I ENTOR ROBE/P7 60/9/1 DOAA40 J. AA 5/651? CHARLES E. ROM/NE AGENT R. c. KOHRN ETAL 3,211,814

Oct. 12, 1965 R. c. KOHRN ETAL METHOD OF MAKING PLASTIC BOATS 3Sheets-Sheet 2 Original Filed March 20, 1958 will!!! IIIIIIIII 1 ROM/NEAGENT 1965 R. c. KOHRN ETAL 3,211,814

METHOD OF MAKING PLASTIC BOATS Original Filed March 20, 1958 3Sheets-Sheet 3 INVENTORS 2/ BY CHARZ Ed F'- ROM/NE AGENT United StatesPatent C) 3,211,814 METHOD OF MAKING PLASTIC BOAT Robert C. Kohrn,Cranston, KL, and Donald J. Kleiber, Norwood Park, and Charles F.Romine, Wheaton, Ill., assignors to United States Rubber Company, NewYork, N.Y., a corporation of New Jersey Original application Mar. 20,1958, Ser. No. 722,814, now Patent No. 3,070,817, dated Jan. 1, 1963.Divided and this application Nov. 6, 1961, Ser. No. 150,574

3 Claims. (Cl. 264-45) This application is a division of our copendingapplication Serial No. 722,814, filed Mar. 20, 1958, now US. Patent3,070,817.

This invention relates to a method of making a boat. More particularlyit relates to a method of making a boat of plastic material embodyingintegral flotation means in the hull.

In accordance with the invention, there is first assembled a laminatecomprising a core of expandable plastic material and outer sheets ofnon-expandable plastic material. Such laminate is heated to cause theplies to bond together and the core to expand. The laminate is thenshaped into a boat hull while in a heated, highly plastic condition,with the aid of a form or forms having shape of the desired hull.

The invention will be described in detail with reference to theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a lay-up of plastic sheets suitablefor use in the invention;

FIG. 2 is a similar view of the lay-up of FIG. 1, on a smaller scale,being heated in a press for the purpose of laminating and curing thesheets and simultaneausly decomposing a blowing agent contained in thecore sheet;

FIG. 3 is a view similar to FIG. 1, showing the laminate after removalfrom the press and after expansion of the core;

FIGS. 4 and 5 are, respectively, longitudinal and end views of thelaminated sheet rotatably supported in a heating device;

FIG. 6 is a plan view of the laminate mounted in the rotatable support;

FIGS. 7 and 8 are, respectively, longitudinal and transverse views ofthe laminate in a heated condition in position Within a shaping devicepreparatory to shaping;

FIGS. 9 and 10 are similar, respectively, to FIGS. 7 and 8, but show thelaminate in contact with the shaping member to form a boat hull;

FIG. 11 is a longitudinal sectional view of the formed boat hull withcertain structural members added to complete the boat;

FIG. 12 is a transverse sectional view, on a larger scale, of the boatof FIG. 11; and

FIG. 13 is a view similar to FIG. 1, of a modified lay-up suitable foruse in the invention.

The form of the invention described in detail involves an open dinghy,but it will be understood that other kinds of boats, having decking,cabins, bulkheads, or other desired provisions for strengthening thehull or affording shelter, may be made by essentially the same method.Such decking and other members may be made of the same material as thehull by the method to be described, or they may be made of any othersuitable desired material.

Referring to the drawings, FIG. 1 shows a lay-up or laminate 10comprising an inner core 11 of a curable or vulcanizable plasticmaterial, preferably a mixture of a major proportion of a hard, plasticmaterial (such as styrene-acrylonitrile resin, with or without polyvinylchloride resin) and a minor proportion of a rubbery material compatibletherewith (such as butadiene-acrylonitrile rubber, with or without smallamounts of other rubbery materials such as polybutadiene, butadiene styrene rubber or natural rubber). The core 11 contains curatives orvulcanizing agents (such as sulfur, preferably along with anaccelerator) which act on the rubbery constituent of the core and causeit to be converted by heat into a strong, solvent-resistant, substance.The core composition further includes a blowing agent, that is, asubstance capable of turning into a gas or vapor or generating a gas orvapor at elevated temperature, thus forming a large number of smallpores or cells in the body of the core, so that the eifective density ofthe core is very much reduced, and the core is thus rendered exteremelybuoyant. Any suitable blowing agent (of which there are many described,for example, in Modern Plastics Encyclopedia Issue, 1956, at pages351-2) may be used. The composition from which the core is made may bemixed in conventional rubber or plastic mixing machinery in accordancewith conventional practice and may be formed into a sheet 11 by anysuitable method, such as calendering. Particularly preferred gum plasticblends are those based on a minor proportion (e.g. 10 to 49 parts) of arubber such as butadiene-acrylonitrile copolymer rubber and a majorproportion (e.g. to 51 parts) of a resin such as styrene-acrylonitrileresin or mixtures of styrene-acrylonitrile resin with a vinyl chlorideresin such as polyvinyl chloride or the like (in ratio of, for example,10 parts of styrene-acrylonitrile resin to 1 to 10 parts of polyvinylchloride). A specific example of a suitable formulation for the core isas follows:

Core: Parts Styrene-acrylonitrile resin 7O Butadiene-acrylonitrilerubber 25 Plasticizer 5 Antioxidant 3.1 Stearic acid l Zinc oxide 3Benzothiazyl disulfide 0.5 Sulfur 1.6 Blowing agent 15 Any suitableconventional plasticizer (such as the liquid butadiene-acrylonitrilecopolymer sold under the trade name Hycar 1312) may be used, as may anysuitable conventional antioxidant (such as the diphenylamineacetonecondensation product known as BLE). As will be understood by thoseskilled in the art of compounding rubber and plastics, other vulcanizingingredients than those shown may be used. Any suitable conventionalblowing agent (such as p,p'-.oxybis(benzenesulfonyl hydrazide) may beused. The proportions of the various ingredients are in general notcritical,'and may be suitably varied as desired. For a small boat, thethickness of the core sheet might typically be about 0.1 (beforeexpansion).

On each side of the core layer 11 there are substrate layers 12, 13 thatare usually less thick (they might, for example, have a thickness ofabout 0.05" for a small boat) than the core. The substrate layers may befabricated from essentially the same ingredients as the core (exceptthat no blowing agent is included) and their function is to provideprotection and strength for the 3 core. An example of a suitableformulation is as follows:

Substrate Parts Styrene-acrylonitrile resin 59.5 Butadiene-acrylonitrilerubber 21.3 Plasticizer (as for the core, above) 4.2 Antioxidant (as forthe core, above) 2.6 Stearic acid 0.8 Zinc oxide 2.5 Benzothiazyldisulfide 0.4 Sulfur 1.15 Polyvinyl chloride Plasticizer for polyvinylchloride (e.g. dioctyl phthalate) 1.8 Calcium stearate 0.1 Stabilizerfor polyvinyl chloride (e.g. cadmium stearate) 0.5

Colored pigments-as desired.

Again, other suitable compounding ingredients may be substituted forthose shown, in any appropriate desired amounts to confer specificproperties of strength, flexibility, stiffness, color etc.

To the outer side of each substrate layer there are applied skin layers14, 15, having a thickness of, for example, 0.015, composed of aflexible, adherent material that is highly resistant to ultra-violetlight, to oxidation, abrasion, ozone, and to weathering. The skin can beprepared in bright colors. Such skin layers are preferably comprised inlarge part of an elastomeric material having little or no unsaturation,such as chlorosulfonated polyethylene, butyl rubber (butyl rubber may beregarded as a substantially saturated rubber for the present purpose),polyisobutylene, polychloroprene, etc. Preferred compositions for theskin layers are based on approxiinately equal parts of chlorosulfonatedpolyethylene and butadiene-acrylonitrile rubber (or -80 parts ofchlorosulfonated polyethylene in correspondingly 80-20 parts of thenitrile rubber). An example of one suitable formulation is as follows:

Skin: Parts Chlorosulfonated polyethylene elastomer 50Butadiene-acrylonitrile rubber 50 Polyethylene 1.5 Hydrogenated rosin1.25 Stearic acid 0.5 Magnesia 5.0 Zinc oxide 1.5 Titanium dioxidepigment 40.0 Silica filler 15.0 Hydrocarbon oil softener 1.25 Sulfur0.75 Benzothiazyl disulfide 0.25 Dipentamethylene thiuram tetrasulfide0.375

Colored pigments-as desired.

In the above examples, thermosetting resins, such as phenolic resins,may supplement or partially replace the thermoplastic resins(styrene-acrylonitrile resin, polyvinyl chloride resin) employed. Otherconventional rubber-resin mixtures, such as those disclosed in FrenchPatent 1,134,141 issued July 19, 1955, may be employed. The skinmaterial must adhere firmly to the underlying layer, and nitrile rubberis included for this reason in the preferred skin.

In place of the lay-up 10 there may be employed a modified lay-up 16(FIG. 13) in which there are applied to the outer surfaces of the lay-upadditional layers of skin 17, 18 consisting essentially of asubstantially saturated elastomer so that it is even more resistant toultra-violet light, such as chlorosulfonated polyethylene, compoundedfor vulcanization in accordance with conventional practice. The core 19,substrates 20, 21 and intermediate skins 22, 23 of the lay-up 16 may beformulated in the same manner as the corresponding layers of the lay-up10. The modified lay-up provides a laminate that is unusually resistantto ultraviolet light.

It will be understood that any given layer of the layup may in fact becomposed of several plied-up sheets, instead of being a single sheet asshown in the drawing for clarity.

The lay-up is somewhat greater in length and width than the desiredlength and beam of the boat. The layup is placed on a lower platen 25 ina conventional heated press 26, within a confining ring 27 extendingaround the periphery of the lay-up. A cover plate 28 resting on theupper surface of the lay-up and of the ring serves to complete a closedmold cavity for the lay-up. The lay-up is heated under pressure to causeadhesion of the various layers to each other, thereby forming anintegral laminate. Instead of curing the laminate in a press, it may beheated under pressure in a vulcanizer or autoclave, for example in anatmosphere of open steam. The heating is carried out for a time andtemperature sufficient to bond together the plies and to cure therubbery constituents of the laminate substantially completely, andsufiicient to decompose the blowing agent in the core. Because thelaminate is maintained under pressure at this stage the core does notblow or expand a great deal, but the gas generated by decomposition ofthe blowing agent simply remains in solution or as compressed bubbleswithin the core composition. Pressures on order of 200 p.s.i. willprevent substantial increase in thickness during the cure. It ispreferred to use a pressure of about 65 p.s.i. to obtain some expansionin thickness during the cure. With the particular compositionsexemplified above, heating at a temperature of about 300 F. for a periodof about 30 minutes gives satisfactory results, although other suitabletemperatures, pressures, and times may of course be used, as will beunderstood by those skilled in the rubber and plastics arts. If thelaminate is cured against a grained surface, the grain will remainthrough the subsequent forming operation to give an attractive surface.

The press is opened or vulcanizer pressure reduced while the laminate isstill hot, whereupon the gas previously generated by the blowing agentexpands the core of the laminate to much more than its originalthickness, as shown in FIG. 3. This now cellular core 11 typically has adensity of only about 15 pounds per cubic foot. Expansion occurssubstantially only in the direction of thickness of the core, becausethe length and width of the laminate are essentially fixed by the nowintegral and vulcanized outer layers of the laminate. The composition ofthe core, that is, the relative proportions of rubbery and thermoplasticmaterials, and the kind and quantity of vulcanizing agents for therubbery constituent, as well as the conditions of heating in the press,are such that the core is able to expandwhile it is in a heatedcondition, even though it has been previously vulcanized. In otherwords, the composition and processing of the core are such that it stillretains a certain amount of thermoplasticity, even though it has enoughstrength (by reason of the vulcanized rubbery component therein) toretain the gas in predominantly closed cells under the conditions of theexpansion. In the composition illustrated, proper expansion is obtainedwhen the curing agent (sulfur) amounts to from about 0.25 to about 1.5parts (per parts of rubber plus resin). The preferred overall density ofthe laminate is about 30 pounds per cubic foot.

The thus-expanded laminate may then be cut to the approximate verticallyprojected profile of the boat (if this has not been done previously) andbolted into a frame 30 (FIGS. 4, 5 and 6) having such outline. The frame30 is rotatably supported below a bank of radiant heaters 31. The frameis slowly rotated while heating the laminate to a temperature (erg.about 300 P.) such that it is readily deformable and begins to sag ofits own weight (as illustrated in FIGS. 7 and 8). Such rotation insuresuniform heating throughout the entire thickness of the laminate, andmakes it possible to carry out properly the now to be described formingoperation.

The frame 30, bearing the soft, deformable heated laminate 10 is nowtransferred to a stand 33 disposed below a male mold 34 having the shapeof the interior surface of the boat hull, and adapted to be raised orlowered at will with the aid of an hydraulic cylinder 35 or equivalentconventional means. To aid in the forming operation the surface of themold is provided with holes 36 which communicate, through the hollowinterior of the mold, with a flexible connection 37 to a source ofvacuum (not shown).- The mold is caused to descend slowly onto the soft,thermoplastic laminate, while applying vacuum, thus causing the laminateto be drawn uniformly into the shape of the mold, as shown in FIGS. '9and 10. By employing the compositions and procedure described it ispossible to thus vacuum draw or mold the laminate into the compoundcurved shape of a boat hull uniformly without undesired distort-ion orlocal thinning out of the laminate. The shaped hull soon becomes cooland rigid enough to hold its shape whereupon it is removed, trimmed, andany desired parts are added to complete the boat (as shown in FIGS. 11and 12) such as wooden gunwa'les 40, keel 41, seats 42, etc.

Many advantages of the invention will be evident to those skilled in theart. The boat is safe and of high quality, and has eminentserviceability and long lasting attractive appearance. The boatwithstands weather, ultraviolet light and atmospheric gases, and retainsits strength under all normal conditions of exposure to heat and cold.It is not adversely affected by humidity, nor by continuous ordiscontinuous salt or fresh water immersion. It withstands abrasion (wetor dry), flexing, vibration, and fatigue. It is impact resistant,withstands heavy weight loads, as well as pounding and shock. It is notharmed by gasoline spillage, nor by oil spillage or oil pickup fromcontaminated water. It withstands marine worms, marine growth, as wellas dry or damp rot, mildew, fungus and bacteria. Difiiculties fromshrinking or swelling are absent.

The hull of the present boat may be made seamless, and is self-buoyanteven when punctured because of the cellular nature of the core. Themethod of making the boat is convenient and economical, and leads to awellshaped boat with a minimum of manipulation.

Having thus described our invention, What We claim and desire to protectby Letters Patent is:

1. A method of making a boat comprising providing a flat core membersheet which is at least as large as the vertically projected profile ofthe desired boat, the said core sheet being a blend of (A) a majorproportion of a thermoplastic resin selected from the group consistingof styrene-acrylonitrile copolymer resin and mixtures ofstyrene-acrylonitrile resin with polyvinyl chloride resin, with (B) aminor proportion of a rubbery butadiene-acrylonitrile copolymer, saidblend containing a vulcanizing agent and a blowing agent, laying up, oneach face of said core sheet, a non-expandable structural member sheetwhich is also a blend of a major proportion of the said resinousmaterial and a minor proportion of the said rubbery material, and whichalso contains a vulcanizing agent 'but no blowing agent, heating theresulting lay-up in the flat under pressure to laminate said sheets intoa seamless integral whole and to decompose the said blowing agent andvulcanize the said rubbery material, releasing the pressure while theresulting laminate is still hot, whereby the said core sheet expands toform a cellular material that is relatively thick in comparison to theoverlying solid sheets, thereafter reheating the resulting integrallaminate to a temperature at which it is readily deformable, and drawingthe heated laminate into conformity with a mold having the shape of thedesired boat, to form the laminate into a boat in which the bottom andentire sides of the boat are of a seamless, self-buoyant andstructurally strong, single piece.

2. A method of making a boat comprising providing a flat core membersheet which is at least as large as the vertically projected profileofthe desired boat, the said core sheet being a blend of (A) a majorproportion of a thermoplastic resin selected from the group consistingof styrene-acrylonitrile copolymer resin and mixtures ofstyrene-acrylonitrile resin with polyvinyl chloride resin, with (B) aminor proportion of a rubbery butadiene-acrylonitrile copolymer, saidblend containing a vulcanizing agent and a blowing agent, laying up, oneach face of each core sheet, a non-expandable structural member sheetwhich is also a blend of a major proportion of the said resinousmaterial and a minor proportion of the said rubbery material, and whichalso contains a vulcanizing agent but no blowing agent, thereafterapplying to each face of the lay-up a continuous protective skin layerwhich is a saturated elastomer, heating the resulting lay-up in the fiatunder pressure to laminate said sheets into a seamless integral wholeand to decompose the said blowing agent and vulcanize the said rubberymaterial, releasing the pressure while the resulting laminate is stillhot, whereby the said core sheet expands to form a cellular materialthat is relatively thick in comparison to the overlying solid sheets,thereafter supporting the laminate for rotation about a horizontal axispassing longitudinally through the laminate, disposing thethus-supported laminate in proximity to a source of radiant heat,rotating the laminate about said axis while so disposed, whereby thelaminate becomes heated throughout substantially without saggingundesirably out of shape during such heating, and thereafter drawing theheated laminate into conformity with a mold having the shape of thedesired boat, to form the laminate into a boat in which the bottom andentire sides of the boat are of a seamless, self buoyant andstructurally strong, single piece.

3. A method of making a rigid shaped laminate comprising providing acontinuous fiat core member sheet which is at least as large as thevertically projected profile of the desired shaped laminate, the saidcore sheet being an unblown blend of a major proportion of athermoplastic resinous material and a minor proportion of a rubberymaterial compatible therewith, said blend containing a blowing agent,laying up, on each face of said core sheet, an overlying solidnon-expandable structural member sheet which is also a blend of a majorproportion of the said resinous material and a minor proportion of thesaid rubbery material but which contains no blowing agent, heating theresulting lay-up in the flat under pressure to laminate said sheets intoa seamless integral whole and to decompose the said blowing agent torelease gas, expanding the said core sheet by the action of saidreleased gas to form a cellular material that is relatively thick incomparison to the overlying solid sheets, thereafter drawing theexpanded laminate, while heated to a temperature at which it is readilydeformable, into conformity with a mold having the desired shape, toform the laminate into a seamless, structurally strong, single piecehaving the desired shape.

References Cited by the Examiner UNITED STATES PATENTS 2,642,920 6/ 53'Simon et al.

2,956,310 10/ 60 Roop et al.

2,979,835 4/ 61' Scholl.

3,003,576 10/61 Dodge 154-492 XR 3,007,208 1 1/61 Urban 15679 3,124,6263/64 Grahm et al. 156-79 EARL M. BERGERT, Primary Examiner. HAROLDANSHER, CARL F. Examiner

1. A METHOD OF MAKING A BOAT COMPRISING PROVIDING A FLAT CORE MEMBERSHEET WHICH IS AT LEAST AS LARGE AS THE VERTICALLY PROJECTED PROFILE OFTHE DESIRED BOAT, THE SAID CORE SHEET BEING A BLEND OF (A) A MAJORPROPORTION OF A THERMOPLASTIC RESIN SELECTED FROM THE GROUP CONSISTINGOF STYRENE-ACRYLONITRILE COPOLYMER RESIN AND MIXTURES OFSTYRENE-ACRYLONITRILE RESIN WITH POLYVINYL CHLORIDE RESIN, WITH (B) AMINOR PROPORTION OF A RUBBERY BUTADIENE-ACRYLONITRILE COPOLYMER, SAIDBLEND CONTAINING A VULCANIZING AGENT AND A BLOWING AGENT, LAYING UP, ONEACH FACE OF SAID CORE SHEET, A NON-EXPANDABLE STRUCTURE MEMBER SHEETWHICH IS ALOS A BLEND OF A MAJOR PROPORTION OF THE SAID RESINOUSMATERIAL AND A MINOR PROPORTION OF THE SAID RUBBERY MATERIAL, AND WHICHALSO CONTAINS A VULCANIZING AGENT BUT NO BLOWING AGENT, HEATING THE